With reference to a conventional cooling structure of a power semiconductor device, for example, Japanese Patent Laying-Open No. 2004-349324 (Patent Document 1) discloses a direct water-cooled power semiconductor module structure which is aimed at achieving a high heat transfer coefficient and improving the cooling efficiency. According to Patent Document 1, stripe-shaped cooling fins are formed on a surface opposite to a surface where a power semiconductor device is mounted.
Japanese Patent Laying-Open No. 2002-368470 (Patent Document 2) discloses a cooling apparatus of a heat generating body which is aimed at cooling the heat generating body sufficiently and to an approximately uniform temperature. Furthermore, Japanese Patent Laying-Open No. 2003-23281 (Patent Document 3) discloses a cooling apparatus which is aimed at increasing the discharged air volume by an electric fan to cool a heat generating body such as a semiconductor package efficiently and effectively. The cooling apparatuses disclosed in Patent Documents 2 and 3 are air-cooled type.
Japanese Patent Laying-Open No. 2002-46482 (Patent Document 4) discloses a heat sink-type cooling apparatus which is aimed at enhancing the heat radiating effect of fins without upsizing them. The heat sink-type cooling apparatus disclosed in Patent Document 4 has a passage through which a coolant flows. Within the passage, a fin group is placed having a plurality of fins arranged in parallel to a flow direction of the coolant and aligned in a direction of the thickness of the fins. The fins of fin groups adjacent to each other in the flow direction of the coolant are arranged so as to be displaced from each other in the direction of the thickness of the fins.
In the cooling structures disclosed in the above-described Patent Documents, a plurality of fins are set up with a spacing therebetween in order to improve the cooling efficiency. The fins are, however, arranged on a path along which a cooling medium flows. Therefore, in a case where the cooling water is used as the cooling medium, the fins and the cooling water flowing through the cooling water passage collide with each other. In this case, when all of the fins collide with the cooling water at the same position in the flow direction of the cooling water, a collision reaction force increases and a vortex flow is generated in the cooling water flow. As a result, a pressure loss of the cooling water flow may significantly increase and the power semiconductor device may not be able to be efficiently cooled.